The health benefits associated with polyunsaturated fatty acids [“PUFAs”], especially ω-3 and ω-6 PUFAs, have been well documented. In order to find ways to produce large-scale quantities of ω-3 and ω-6 PUFAs, researchers have directed their work toward the discovery of genes and the understanding of the encoded biosynthetic pathways that result in lipids and fatty acids.
A variety of different hosts including plants, algae, fungi, stramenopiles and yeast are being investigated as means for commercial PUFA production. Genetic engineering has demonstrated that the natural abilities of some hosts, even those natively limited to linoleic acid [“LA”; 18:2 ω-6] or α-linolenic acid [“ALA”; 18:3 ω-3] fatty acid production, can be substantially altered to result in high-level production of various long-chain ω-3/ω-6 PUFAs. Whether this is the result of natural abilities or recombinant technology, production of docosahexaenoic acid [“DHA”; 22:6 ω-3] from docosapentaenoic acid [“DPA”; 22:5 ω-3] may require expression of a Δ4 desaturase. More specifically, most Δ4 desaturase enzymes identified so far have the primary ability to convert DPA to DHA, with secondary activity in converting docosatetraenoic acid [“DTA”; 22:4 ω-6] to ω-6 docosapentaenoic acid [“DPAn-6”; 22:5 ω-6].
Based on the role Δ4 desaturase enzymes play in the synthesis of DHA, there has been considerable effort to identify and characterize these enzymes from various sources. Numerous Δ4 desaturases have been disclosed in both the open literature and the patent literature. Some examples include: Euglena gracilis (SEQ ID NO: 13; GenBank Accession No. AY278558; Meyer et al., Biochemistry, 42(32):9779-9788 (2003)); Thalassiosira pseudonana (SEQ ID NO:37; GenBank Accession No. AAX14506; Tonon et al., FEBS J., 272(13):3401-3412 (2005)); Thraustochytrium aureum (SEQ ID NO:14; GenBank Accession No. AAN75707); Thraustochytrium sp. (GenBank Accession No. CAD42496; U.S. Pat. No. 7,087,432); Schizochytrium aggregatum (SEQ ID NO:41; Int'l. App. Pub. No. WO 2002/090493); Pavlova lutheri (SEQ ID NO:42; GenBank Accession No. AAQ98793); and, Isochrysis galbana (SEQ ID NO:43; GenBank Accession No. AAV33631; Pereira et al., Biochem. J., 384(2):357-366 (2004); Int'l. App. Pub. No. WO 2002/090493). There is need for the identification and isolation of additional genes encoding Δ4 desaturases that will be suitable for heterologous expression in a variety of host organisms for use in the production of ω-3/ω-6 fatty acids.
Applicants have solved the stated problem by isolating genes encoding Δ4 fatty acid desaturases from Eutreptiella cf—gymnastica CCMP1594.